Novel organometallic luminescent materials and organic electroluminescent device containing same

ABSTRACT

An organometallic luminescent material selected from the group consisting of the compounds of formulae (I) to (V) of the present invention can emit blue, green and red lights.

FIELD OF THE INVENTION

[0001] The present invention is directed to novel organometallicluminescent materials, and, more particularly, to a novel organometallicluminescent material having the capability of emitting a wide range ofcolors including blue and green light, and high thermal stability, andan organic luminescent device containing same.

BACKGROUND OF THE INVENTION

[0002] Conventional organometallic luminescent compounds used in organicelectroluminescent devices are mostly complexes of di- or trivalentmetals such as zinc and aluminium.

[0003] For example, U.S. Pat. No. 5,456,988 describes 8-hydroxyquinolinecomplexes of zinc, aluminium and magnesium as organic luminescentmaterials; U.S. Pat. No. 5,837,390 discloses magnesium, zinc and cadmiumcomplexes of 2-(o-hydroxyphenylbenzoxazole); Japanese Patent Laid-OpenPublication No. 07-133483 reports luminescent complexes of2-(o-hydroxyphenylbenzoxazole) with divalent metals such as magnesiumand copper; and U.S. Pat. No. 5,529,853, and Japanese Patent Laid-OpenPublication Nos. 06-322362, 08-143548 and 10-072580 disclose divalent ortrivalent metal complexes of 10-hydroxybenzo[10]quinoline.

[0004] The above organometallic luminescent compounds containing adivalent or trivalent metal have relatively loosely bound ligands and anextended system of conjugation. As a result, they are relativelyunstable and emit green or red light but not a blue light.

[0005] Therefore, there has existed a need to develop an organometallicluminescent material having improved stability and light emissioncharacteristics such as the capability of emitting a blue light.

SUMMARY OF THE INVENTION

[0006] Accordingly, it is a primary object of the present invention toprovide a novel organometallic luminescent material having the stabilityand desired emission characteristics, and an organic luminescent devicecontaining same.

[0007] In accordance with the present invention, there is provided anorganometallic luminescent material selected from the group consistingof the compounds of, formulae (I) to (V).

[0008] wherein,

[0009] M¹ and M⁴ are each independently a monovalent or tetravalent.metal selected from the group consisting of Li, Na, K, Zr, Si, Ti, Sn,Cs, Fr, Rb, Hf, Pr, Pa, Ge, Pb, Tm and Md;

[0010] M² is a mono-, di-, tri- or tetravalent metal selected from thegroup consisting of Li, Na, K, Ca, Be, Ga, Zn, Cd, Al, Cs, Fr, Rb, Mg,Mn, Ti, Cu, Zr, Si, Hf, Pr, Pa, Ge, Sn, Pb, Tm and Md;

[0011] M³ is selected from the group consisting of Li⁺, Na⁺, K⁺, Cs⁺,Fr⁺, Rb⁺, Ca²⁺, Be²⁺, Ga³⁺, Zn²⁺, Al³⁺, Mg²⁺, Mn²⁺, Ti²⁺and Cu²⁺;

[0012] R is a hydrogen or C₁-₁₀ alkyl;

[0013] X and Y, which can be the same or different, are 25 independentlya hydrogen, Cl, F, I, Br or SO₃H;

[0014] A is a hydrogen, F, Cl, Br or I;

[0015] B is O, S, Se or Te;

[0016] D is O or S; and

[0017] n is an integer ranging from 1 to 4.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects and features of the present inventionwill become apparent from the following description thereof, when takenin conjunction with the accompanying drawings wherein:

[0019]FIGS. 1a, 1 b and 1 c illustrate schematic diagrams of organicelectroluminescent devices having an organic layer in the form of asingle layer, a double layer or a multilayer, respectively;

[0020]FIG. 2 shows the light emission spectrum of the organometallicluminescent material of Example 1 of the present invention;

[0021]FIG. 3 demonstrates variations of the current density(A/m²)(3-1)and brightness(cd/m²)(3-2) of the electroluminescent device of Example 2of the present invention as a function of applied voltage(V);

[0022]FIGS. 4a and 4 b depict changes in the luminous efficiency(lm/w)of the electroluminescent device of Example 2 with current density(A/m²)and brightness(cd/m²), respectively; and

[0023]FIG. 5 exhibits the electroluminous spectra of theelectroluminescent device of Example 2 of the present invention atvarious applied voltages(V).

DETAILED DESCRIPTION OF THE INVENTION

[0024] The organometallic luminescent materials of the present inventioninclude 8-hydroxyquinoline-metal complexes of formula(I)-8-hydroxyquinoline-5-sulfonate-metal complexes of formula (II),benzoxazole- or benzthiazole-metal complexes of formula(III),benzotriazole-metal complexes of formula (IV), and benzoquinoline-metalcomplexes of formula (V)

[0025] Among the organometallic luminescent materials of the presentinvention, preferred are those listed in Table I. TABLE I Compound γ maxFormula No. M* M₃ X Y A B D n R (nm) color (I) 1 Li — H H — — — 1 H 495bluish green 2 Li — H H — — — 1 CH₃ 490 bluish green 3 Zr — H H — — — 4H 535 light green 4 Zr — H H — — — 4 CH₃ 532 light green (II) 5 Li Li —— H — — 1 H 460 blue 6 Li Na — — H — — 1 H 462 blue 7 Na Li — — H — — 1H 460 blue 8 Na Na — — H — — 1 H 463 blue 9 Zn Li — — H — — 2 H 461 blue10 Zn Na — — H — — 2 H 464 blue 11 Al Li — — H — — 3 H 462 blue 12 Al Na— — H — — 3 H 465 blue (III) 13 Li — — — — O O 1 H 450 blue 14 Na — — —— — O 1 H 455 blue (IV) 15 Li — — — — — O 1 H 508 green 16 Na — — — — —O 1 H 512 green (V) 17 Li — — — — — O 1 H 515 green 18 Na — — — — — O 1H 650 red

[0026] The organometallic luminescent compound of the present inventionmay be prepared by reacting an organic compound that can serve as aligand with an appropriate metal compound in a suitable solvent.

[0027] Exemplary solvents which can be used in the present inventioninclude water, ethanol, methanol, propanol and the like.

[0028] Representative metal compounds that can be used to prepare theorganometallic luminescent compounds of the present invention are LiOH,NaOH, KOH, NaCl, KCl, LiCl, ZrCl₄, SnCl₄, TiCl₄, SiCl₄, BeC₂, MgCl₂,AlC₃, CaCl₂, ZnCl₂ and the like.

[0029] Representative organic compounds which can be used as ligands inthe present invention include 2-(2-hydroxy-phenyl )benzoxazole,8-hydroxyquinoline, 8-hydroxy-quinoline -5-sulfonic acid,2-(2-benzo-triazolyl)-p-cresol, 10-hydroxybenzoquinoline and the like.

[0030] The reaction of the organic and metal compounds to prepare theorganometallic luminescent compound of the present invention may becarried out in a stoichiometric molar ratio which depends on n at atemperature ranging from 25 to 100° C. for 1 to 24 hours.

[0031] In the preparation of 8-hydroxyquinoline-5-sulfonate metalderivative of formula(II), 8-hydroxyquinoline -5-sulfonic acid and asuitable M² compound are reacted to give 8-hydroxyquinoline-5-sulfonatederivatives of formula (VI). Subsequently, the compound of formula(VI)is reacted with a compound of M³ to obtain the 8-hydroxyquinoline-5-sulfonate derivative of formula (II).

[0032] Alternatively, the 8-hydroxyquinoline-5-sulfonate metalderivative of formula(II) may be prepared by a dry process. That is, acompound of formula (VI) and a compound of formula(VII) may be depositedseparately on a substrate and an in-situ reaction thereof may beincurred, e.g., at 150 to 450° C. under a reduced pressure(about 10⁻⁶torr). The metallation of the sulfonic acid group in accordance with thein-situ reaction of scheme 1 accompanies a blue shift in the emittedlight. For example, the maximum wavelength of the emitting light of thecompound of formula(VI) is 510 nm while that of the compound offormula(II) is 460 nm.

[0033] wherein, M², M³ and n have the same meanings as defined above,and Z is a halogen atom or hydroxy group.

[0034] The organometallic complex of the present invention can be usedas a luminescent doping material as well. For example, when it is dopedin an amount of about 2% in a blue light emitting luminescent layer, theemitting light changes from blue to light blue or green. Accordingly, anefficient electroluminescent device capable of emitting a tuned colorcan be prepared.

[0035] The organic luminescent device of the present invention has astructure comprising an organic thin layer in the form of a singlelayer, or in the form of a double layer and multilayer containing a holetransporting layer and/or an electron transporting layer. In this case,the organometallic luminescent material of the present invention can beused alone, or in combination with a polymer or an inorganic material.Further, it may be doped in a polymer to give a fluorescent thin layer.

[0036] An example of the electroluminescent device of the presentinvention contains a single organic layer as shown in FIG. 1a. Thedevice consists of (i) a glass substrate, (ii) a transparent ITO(indiumtin oxides) anode electrode layer, (iii) an organic luminescent layercontaining an organometallic luminescent material of the presentinvention, and (iv) a metal cathode electrode layer. Another example ofthe inventive device has an additional hole transporting layer(iii-1) asshown in FIG. 1b, or a multilayered structure shown in FIG. 1C wherein(iii-2) denotes an additional electron transporting layer. Theelectroluminescent device of the present invention may be operated withdirect or alternative current, while the direct current is preferred.

[0037] The organic luminescent layer of the present invention may beformed by a conventional method including a wet process such as spincoating, and a dry process such as a vapor deposition, vacuum thermaldeposition, sputtering and electron beam deposition method.

[0038] The novel organometallic luminescent compound of the presentinvention is capable of emitting blue, green or red light. The inventivecomplexes containing monovalent metals in particular are excellent bluelight emitting luminescent materials which are stable even at a hightemperature.

[0039] The present invention is further described and illustrated inExamples, which are, however, not intended to limit the scope of thepresent invention.

EXAMPLE 1 Preparation Compound 13

[0040] 2-(2-hydroxyphenyl)benzoxazole and lithium oxide were added to250 ml of ethanol in a molar ratio of 1:1 and the mixture was refluxedat 78° C. for 4 hours. The reaction mixture was filtered and the solventand moisture were removed under a reduced pressure to give2-(2-hydroxyphenyl)benzoxazole-lithium complex of formula(VIII)(compound 13).

[0041]FIG. 2 shows light emission spectrum of the complex thus obtained.

EXAMPLE 2

[0042] Indium-tin-oxide(ITO) was coated on a glass substrate to form atransparent anode layer. The coated substrate was subjected tophotolithography and the patterned ITO glass was cleaned with a solutioncontaining a non-phosphorous detergent, acetone and ethanol.

[0043] A mixture of polyetherimide of formula(IX) and triphenyldiamineof formula(X) in a weight ratio of 50:50 were dissolved in chloroform toa concentration of 0.5 wt %, and the resulting mixture was spin-coatedon the ITO glass to form a hole transporting layer.

[0044] wherein m is an integer of two or higher.

[0045] 2-(2-hydroxyphenyl)benzoxazole-lithium complex obtained inExample 1 was vapor deposited as a luminescent material on the holetransporting layer to a thickness of 20 nm to form an organicluminescent layer, and then, aluminium was vapor deposited to athickness of 500 nm to form a cathode layer. Subsequently, the devicewas packaged to obtain an electroluminescent device.

[0046] The luminescence characteristics of the electroluminescent deviceare shown in FIGS. 3, 4 and 5.

[0047]FIG. 3 illustrates the variation of the current density(A/m²)(3-1)and brightness(cd/m²) of the electroluminescent device thus obtained asa function of the applied voltage(V). The current injection starts atabout 6V, turn on voltage is about 7 to 8V, and the brightness is500cd/m² at 11V.

[0048]FIGS. 4a and 4 b depict the changes in the luminousefficiency(lm/w) of the above electroluminescent device with currentdensity(A/m²) and brightness(cd/m²), respectively. The luminousefficiency is steady at 1.2 lm/W at a current density of 200A/m² andbeyond.

[0049]FIG. 5 exhibits electroluminous spectra of the aboveelectroluminescent device at various applied voltages of 8, 9, 10, 11,12 and 13V. The main peak appears at 456 nm and shoulder peaks areobserved at 430 and 487 nm. The emitted light is blue.

EXAMPLE 3 Preparation of Compounds 5 and 6

[0050]8-hydroxyquinoline-5-sulfonic acid and lithium hydroxide wereadded to 250 ml of ethanol in a molar ratio of 1:1 and the mixture wasrefluxed at 78° C. for 4 hours. The reaction mixture was filtered anddissolved in an excess amount of water. Subsequently, water was removedunder a reduced pressure to obtain lithium complex of8-hydroxyquinoline-(5-sulfonic acid)-(LiQSA).

[0051] LiQSA thus obtained and LiOH(or NaOH) were added to 100 ml ofethanol in a molar ratio of 1:1 and the mixture was reacted at a roomtemperature for 1 hour. Precipitates were separated from the reactionmixture and dried for 24 hours under a reduced pressure to obtain alithium complex of lithium 8-hydroxyquinolinato-5-sulfonate (LiQSLi,Compound 5), or a lithium complex of sodium8-hydroxyquinolinato-5-sulfonate (LiQSNa, Compound 6), respectively.

[0052] The maximum wavelength and emitted colors of the complexes thusobtained were measured and shown in Table I.

EXAMPLE 4 Preparation of Compounds 7 and 8

[0053] 8-hydroxyquinoline-5-sulfonic acid and sodium hydroxide wereadded to 250 ml of ethanol in a molar ratio of 1:1 and the mixture wasrefluxed at 78° C. for 4 hours. The reaction mixture was filtered anddissolved in an excess amount of water. Subsequently, water was removedunder a reduced pressure to obtain 8-hydroxyquinolin-(5-sulfonic acid)sodium complex (NaQSA).

[0054] NaOSA thus obtained and LiOH(or NaOH) were added to 100 ml ofethanol in a molar ratio of 1:1 and the mixture was reacted at a roomtemperature for 1 hour. Precipitates were separated from the reactionmixture and dried for 24 hours under a reduced pressure to obtain asodium complex of lithium 8-hydroxyquinolinato-5-sulfonate (NaQSLi,Compound 7) or a sodium complex of sodium8-hydroxyquinolinato-5-sulfonate (NaQSNa, Compound 8).

[0055] The maximum wavelengths and emitted colors of the complexes thusobtained were measured and shown in Table I.

EXAMPLE 5 Preparation of Compounds 9 and 10

[0056]8-hydroxyquinoline-5-sulfonic acid and zinc chloride (ZnCl₂) wereadded to 250 ml of ethanol in a molar ratio of 2:1 and the mixture wasrefluxed at 78° C. for 4 hours. The reaction mixture was filtered anddissolved in an excess amount of water. Subsequently, water and HCl wereremoved under a reduced pressure to give a zinc complex ofbis(8-hydroxyquinolinato-5-sulfonic acid) (Zn(QSA)₂).

[0057] Zn(QSA)₂ thus obtained and LiOH(or NaOH) were added to 100 ml ofethanol in a molar ratio of 1:2 and the mixture was reacted at a roomtemperature for 1 hour. Precipitates were separated from the reactionmixture and dried for 24 hours under a reduced pressure to obtain a zinccomplex of lithium bis(8-hydroxyquinolinato-(5-sulfonate) (Zn(QSLi)₂,Compound 9), or a zinc complex of sodiumbis(8-hydroxyquinolin-5-sulfonate) (Zn(QSNa)₂, Compound 10).

[0058] The maximum wavelengths and emitted colors of the complexes thusobtained were measured and shown in Table I.

EXAMPLE 6 Preparation of Compounds 11 and 12

[0059]8-hydroxyquinoline-5-sulfonic acid and AlCl₃ were added to 250 mlof ethanol in a molar ratio of 3:1 and the mixture was refluxed at 78°C. for 4 hours. The reaction mixture was filtered and dissolved in anexcess amount of water. Subsequently, water and HCl were removed under areduced pressure to obtain aluminiumtris(8-hydroxyquinolinato-5-sulfonic acid) (Al(QSA)₃).

[0060] Al(QSA)₃ thus obtained and LiOH (or NaOH) were added to 100 ml ofethanol in a molar ratio of 1:3 and the mixture was reacted at a roomtemperature for 1 hour. Precipitates were separated from the reactionmixture and dried for 24 hours under a reduced pressure to obtain analuminium complex of lithium tris(8-hydroxyquinolin-(5-sulfonate)(Al(QSLi)₃₁ Compound 11), or an aluminium complex of sodiumtris(8-hydroxyquinolin-5-sulfonate) complex (Zn(QSNa)₃).

[0061] The maximum wavelengths and emitted colors of the complexes thusobtained were measured and shown in Table I.

EXAMPLE 7 Preparation of Compound 14

[0062] 2-(2-hydroxyphenyl)benzoxazole and NaOH were added to 250 ml ofethanol in a molar ratio of 1:1 and the mixture was refluxed at 78° C.for 4 hours. The reaction mixture was filtered and the solvent andmoisture were removed under a reduced pressure to obtain2-(2-hydroxyphenyl)-benzoxazole -sodium complex.

[0063] The maximum wavelength and emitted color of the complex thusobtained were measured and shown in Table I.

EXAMPLE 8 Preparation of Compounds 15 and 16

[0064] 2-(2-hydroxybenzotriazole)-p-cresol and LiOH(or NaOH) were addedto 250 ml of ethanol in a molar ratio of 1:1 and the mixture wasrefluxed at 78° C. for 4 hours. The reaction mixture was filtered andthe solvent and moisture were removed under a reduced pressure to give2-(2-hydroxybenzotriazole)-p-cresol-lithium complex (LiBTZC, Compound15), or 2-(2-hydroxybenzotriazole)-p-cresol -sodium complex(NaBTZC,Compound 16).

[0065] The maximum wavelengths and emitted colors of the complexes thusobtained were measured and shown in Table I.

EXAMPLE 9 Preparation of Compounds 17 and 18

[0066] 10-hydroxyquinoline and LiOH (or NaOH) were added to 250 ml ofethanol in a molar ratio of 1:1 and the mixture was refluxed at 78° C.for 4 hours. The reaction mixture was filtered and the solvent andmoisture were removed under a reduced pressure to obtain10-hydroxyquinoline-lithium complex(LiBQ, Compound 17), or10-hydroxyquinoline-sodium complex(NaBQ, Compound 18).

[0067] The maximum wavelengths and emitted colors of the complexes thusobtained were measured and shown in Table I.

EXAMPLE 10 Preparation of Compound 3

[0068] 8-hydroxyquinoline and ZrCl₄ were added to 250 ml of ethanol in amolar ratio of 4:1 and the mixture was refluxed at 78° C. for 4 hours.The reaction mixture was filtered and the solvent, HCl and moisture wereremoved under a reduced pressure to obtaintetra(8-hydroxyquiloninato)-zirconium complex (ZrQ₄, Compound 3).

[0069] The maximum wavelength and emitted color of the complex thusobtained were measured and shown in Table I.

[0070] As can be seen from the above result, the organometallicluminescent material of the present invention exhibits blue, green orred light emission. Therefore, an electroluminescent device containingthe same is capable of exhibiting a full range of colors in the visibleregion with a high efficiency.

[0071] While the embodiments of the subject invention have beendescribed and illustrated, it is obvious that various changes andmodifications can be made therein without departing from the spirit ofthe present invention which should be limited only by the scope of theappended claims.

What is claimed is:
 1. An organometallic luminescent material selectedfrom the group consisting of the compounds of formulae (I) 5 to (V):

wherein, M¹ and M⁴ are each independently a monovalent or tetravalentmetal selected from the group consisting of Li, Na, K, Zr, Si, Ti, Sn,Cs, Fr, Rb, Hf, Pr, Pa, Ge, Pb, Tm and Md; M² is a mono-, di-, tri- ortetravalent metal selected from the group consisting of Li, Na, K, Ca,Be, Ga, Zn, Cd, Al, Cs, Fr, Rb, Mg, Mn, Ti, Cu, Zr, Si, Hf, Pr, Pa, Ge,Sn, Pb, Tm and Md; M³ is selected from the group consisting of Li⁺, Na⁺,K⁺, Cs⁺, Fr⁺, Rb⁺, Ca²⁺, Be²⁺, Ga³⁺, Zn²⁺, Al³⁺, Mg²⁺, Mn²⁺, Ti²⁺andCu²⁺; R is a hydrogen or C₁- alkyl; X and Y, which can be the same ordifferent, are independently a hydrogen, Cl, F, I, Br or SO₃H; A is ahydrogen, F, Cl, Br or I; B is O, S, Se or Te; D is O or S; and n is aninteger ranging from 1 to
 4. 2. A process for preparing a complex offormula(II) by vapor depositing 8-hydroxylquinolin-5-sulfonic acid metalcomplex of formula(VI) and subjecting the deposited complex to anin-situ reaction with a compound of formula(VII):

M³Z  (VII) wherein, M², M³, R and n have the same meanings as defined inclaim 1, and Z is a halogen atom or hydroxy group.
 3. Anelectroluminescent device which comprises an organic luminescent layercontaining the organometallic luminescent material defined in claim 1.4. The device of claim 3 wherein the organometallic luminescent materialis present alone, or in combination with a polymer or an inorganicmaterial, or in the form of a dopant in a polymer.
 5. The device ofclaim 3 wherein the organic luminescent layer is formed by a spincoating, vapor deposition, vacuum thermal deposition, sputtering orelectron beam deposition method.